Vehicle telematics services carried over a public land mobile network (PLMN) or other wireless carrier system present certain challenges unique to the mobile vehicle application. For example, some vehicle telematics units (VTU) are designed to permit both voice and data communications over the wireless carrier system using one or more of the various available different transmission technologies, such as 2G CDMA (IS-95), 3G CDMA2000 (IS-2000, 1 XRTT, EVDO), 3G UTMS (W-CDMA, HSPA), 2G/2.5G GSM (GPRS and EDGE). Depending on such things as the technology used, e.g., GSM versus CDMA, the registration or acquisition process required, the frequent movement of the vehicle into and out of a home PLMN (HPLMN), the availability of one data transmission protocol versus another, and the particular type of call being made to or from the vehicle, the VTU may only have one wireless communication protocol available and suitable for use, or may have more than one from which it can select. And while multiple types of wireless transmission may be available at any one time, their associated cost of use can vary making it desirable to judiciously select among them. Similarly, call connection costs associated with data roaming can be significant and it can therefore be desirable to implement connection strategies that minimize roaming and its associated costs.
This can be especially true for vehicle telematics units since, when used, a telematics unit may often be moving (with the vehicle) at a speed that exposes it to an ever-changing cellular landscape, which can include rapidly moving between different cellular networks (wireless carrier systems), including into and out of roaming and home cellular networks.